Caterpillars and Monarchs, Part One

by Josh on August 27, 2011 · 3 comments

in Journal

Very little good can come from letting weeds get out of control in your yard. Not only do the weeds look bad, but they can choke out the desirable plants and seed themselves so the problem keeps getting worse. But in the case of milkweed, all those problems come with a glorious perk.

monarch on deck rail


You may recall that last year someone gave us some monarch chrysalises that we got to hatch in our home. This year, with some careful hunting from my junior entomologists, we found several tiny caterpillars on the milkweed in our yard. We gave a few caterpillars to neighborhood friends and adopted the rest until they were ready to spread their wings.

baby caterpillar on milkweedMonarch butterflies lay their eggs on milkweed plants and then the new caterpillars gorge themselves on the leaves until they have grown big enough to metamorphose. Which brings me to an important detail. Anyone who has read Eric Carle’s The Very Hungry Caterpillar is familiar with caterpillars’ prodigious appetite. But ingestion is only half the story because caterpillars are also very… productive.

caterpillar droppings

With all that digestion, caterpillars grow quickly. In about a week, the tiny caterpillar above will have grown five or six times bigger.

caterpillar on twig

Once the caterpillar gets this large, it starts looking for a place to form its chrysalis. When it finds a suitable spot on a twig or the underside of a leaf it attaches itself from the backside and hangs in an upside curl called “J” formation.

Caterpillar j formation

Now things start to get interesting. Several hours after attaching like this–usually the following morning–the caterpillar forms its chrysalis in a move straight out of a horror movie script. That’s because the chrysalis doesn’t form around the caterpillar– it forms inside it.

The transformation happens very quickly, so it’s easy to miss. When the caterpillar’s colored bands appear blurry and the antennae hang limp, the final molt will soon begin. It starts with the caterpillar’s head splitting open and then caterpillar continues to skin itself, pulling the outer covering up toward the attachment point and exposing the soft blue-green surface of the new chrysalis.

chrysalis emerging from caterpillar skin

The whole process of shedding its skin takes just a minute and shortly after that the firm surface and final shape of the chrysalis will have set.

monarch chrysalis on leaf

The caterpillar remains in the chrysalis about a week transforming into a butterfly. The process of hatching from the chrysalis is just as fascinating as forming the chrysalis– and just as easy to miss. I’ll write about hatching our pet monarchs in part two of this post. Stay tuned!

{ 1 comment… read it below or add one }

Kirsti @Living in Lovely LaLaLand August 29, 2011 at 11:32 am

Your photos are beautiful. I’m excited to see part two!


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